Patent Literature 1 discloses a common mode noise filter comprising: a first magnetic body and a second magnetic body; a non-magnetic body sandwiched between the first magnetic body and second magnetic body; a first coil conductor and a second coil conductor of planar shape which are embedded in the non-magnetic body and positioned on the first magnetic body side and second magnetic body side in the non-magnetic body in a manner facing each other in a non-contact state; a first external terminal connected to one end of the first coil conductor via a first lead conductor; a second external terminal connected to the other end of the first coil conductor; a third external terminal connected to one end of the second coil conductor via a second lead conductor; and a fourth external terminal connected to the other end of the second coil conductor.
With this common mode noise filter, the first lead conductor is present between the first magnetic body and non-magnetic body, and the second lead conductor is present between the second magnetic body and non-magnetic body. Additionally, Fe2O3-based ferrite is used for the first magnetic body and second magnetic body, Cu—Zn ferrite or glass ceramics is used for the non-magnetic body, and silver is used for the first lead conductor, first coil conductor, second coil conductor, and second lead conductor.
In the above, this common mode noise filter is generally mounted on a circuit board, etc., by means of reflow soldering and thus receives considerable thermal shock when reflow-soldered, and once mounted the filter also receives thermal shock when exposed to high temperature or low temperature.
Since this common mode noise filter is structured in such a way that the first lead conductor lies between the first magnetic body and non-magnetic body and the second lead conductor lies between the second magnetic body and non-magnetic body, separation occurs at the following locations when the aforementioned thermal shock is received, due to differences between the coefficient of linear expansion of the first lead conductor and coefficients of linear expansion of the first magnetic body and non-magnetic body and also between the coefficient of linear expansion of the second lead conductor and coefficients of linear expansion of the second magnetic body and non-magnetic body:    interface between the first lead conductor and first magnetic body,    interface between the first lead conductor and non-magnetic body,    interface between the second lead conductor and second magnetic body, and    interface between the second lead conductor and non-magnetic body.Because of this separation, delamination occurs at the following locations to cause filter characteristics such as the impedance characteristics or the like to deteriorate:    interface between the first magnetic body and non-magnetic body, and    interface between the second magnetic body and non-magnetic body.